This invention relates generally to the detection of objects using radar techniques. More specifically, the present invention relates to the detection of the centroid of an object in addition to merely detecting the object's presence.
The word centroid as used herein is intended to encompass the central area of an object and not merely the precise geometric center. Many varied techniques may be employed to detect the mere presence of an object. However, the detection of the centroid of an object presents a unique set of problems. A centroid detector must distinquish an object from a background environment, yet remain insensitive to the object's periphery. When an object may exhibit many different shapes, sizes, velocities, and angles of approach and departure, problems are encountered.
Some apparatus incorporate heat sensing to detect the central area of an object. Such detectors may be responsive to any heat generating object, and therefore indicate the centroid of objects which are not intended to be detected. For example, if an application desires to detect vehicles, then an apparatus which detects both vehicles and animals may not provide an acceptable solution. Furthermore, detection devices are responsive to heat rather than an object's geometry. The hotter areas of an object, such as a vehicle engine, need not be in the center of the object so heat detection techniques may not reliably indicate the centroid of an object.
Radar techniques may provide an answer to the problems encountered with heat detection. A centroid detection apparatus employing radar techniques is most responsive to metallic objects, and the location of heat generated by an object is immaterial. Thus, applications which wish to detect the centroid of a vehicle may find a radar technique superior to heat detection techniques.
On the other hand, the use of a radar technique in a centroid detection apparatus poses another set of problems. For example, a centroid detection apparatus must distinquish the central area of an object from the object's periphery in spite of a large variation in object size, speed, environment, and proximity to the apparatus. Furthermore, the centroid detection apparatus must not respond to specular returns. Specular returns occur when relatively flat metallic surfaces are presented substantially perpendicular to a radar's illumination. The reflected energy represents a specular return which may exhibit an amplitude as great as two orders of magnitude greater than a normal reflection. While a specular return may not pose a large problem for the mere detection of an object's presence, its disproportionately large amplitude must not cause a centroid detection apparatus to provide a false indication of the object's centroid. Further, well known radar techniques such as frequency agility, pulse compression, range gate jitter, beam weeping, or range gating either do not eliminate specular returns or require excessive cost to implement.